1. Field of the Invention
The present invention relates to a soil compacting device having a vibration generator that impinges on a soil contact element, as well as to a method for controlling the vibration generator.
2. Description of the Related Art
Soil compacting devices, for example vibration plates or vibrating rollers, are known in which a soil contact element, such as a plate or the tire of a roll, receives a vibration produced by a vibration generator.
The compacting of the soil takes place in that the soil compacting device travels over it once or a plurality of times, resulting in a modification of the solidity of the soil, and thus also a modification of its vibration characteristic. If the soil is already highly compacted and the compacting power delivered by the soil compacting device is great, the soil compacting device can begin to xe2x80x9cjump,xe2x80x9d in that the soil contact plate or roll tire lifts off the soil after each contact with the soil. This not only represents a waste of energy, but is also disadvantageous for the compacting that has already taken place, because local loosenings of the soil can result. Moreover, a jumping of the soil compacting device leads to considerable stress on the operator of the device.
From WO-A-98-17865 and WO-A-95-10664, vibration compacting devices are known in which the operational state of jumping is automatically reacted to by modifying the vibration produced by the vibration generator.
In the devices or methods known from the prior art, the frequency of the vibration generator is standardly adapted to the previously determined soil characteristics. For this purpose, for example in WO-A-98-17865 the state of the soil is determined through the costly evaluation of various measurement signals. In particular, for this purpose it is necessary to determine the movement of the soil contact element, which is a component of a vibrating lower mass. Furthermore, the set frequency and the precise position of the vibration generator must be measured.
In addition, soil compacting devices are known in which the amplitude of the vibration produced by the vibration generator is reduced in such a way that jumping of the soil compacting device can no longer occur. However, the limitation of the amplitude at a predetermined frequency has the result that it is no longer possible to use the entire available drive power for which the vibration generator is designed for the compacting of the soil. The consequence of this is a correspondingly lower operational efficiency.
FIG. 3 shows a known vibration plate used as a soil compacting device, which can be guided by an operator at a drawbar 1. A drive 2, appertaining to an upper mass, drives a vibration generator 3 appertaining to a lower mass, and this vibration generator produces a vibration that is communicated to a soil contact plate 4. Vibration generator 3 is standardly a one-shaft or two-shaft generator, in which one or more imbalance masses are correspondingly distributed on one or two shafts. The design of such a vibration plate is known, so that further description is not required.
Vibrating rollers used as soil compacting devices are also constructed in a similar, known manner.
The invention is based on the object of indicating a soil compacting device comprising a vibration generator, as well as a method for controlling the vibration generator, in which an optimal exploitation of the power supplied by the drive is ensured.
According to the present invention, this object is achieved through a soil compacting device according to claim 1, and through a method according to claim 11.
Advantageous further developments of the present invention are defined in the dependent claims.
The basic idea of the present invention is to provide respective control units for the amplitude and for the frequency of the vibration produced by the vibration generator, and to realize these using simple means. Above all, in the interaction of the two control units it is possible to optimally exploit the available drive power, for example of a drive motor, without the occurrence of the undesired xe2x80x9cjumpingxe2x80x9d of the soil compacting device.
In the combination according to the present invention of amplitude controlling and frequency controlling, this is enabled in that the vibration amplitude is always kept within the region bordering on jumping. If this boundary region changes, for example making it necessary to reduce the amplitude of the vibration, the frequency control unit tracks this by increasing the vibration frequency correspondingly, in order to use the drive energy that becomes available as a result of the reduction of the vibration amplitude in the form of a higher frequency. In this way, the drive energy can be used as completely as possible for the soil compacting, without the beginning of jumping on the part of the soil compacting device.
The controlling of the amplitude is based on the principle that whenever a jumping of a soil contact element is recognized, the amplitude is reduced. The monitoring of whether the soil contact element is jumping takes place continuously, or regularly, in the context of a predetermined clock pulse. After a modification of the amplitude, there thus takes place a new determination of the state of vibration of the soil contact element. If the soil contact element is still jumping, a further reduction of the amplitude takes place. However, if no jumping is recognized, the amplitude is not held constant at approximately the existing value, but rather is again increased, though with a smaller gradient. As a consequence, the amplitude is constantly being modified, either by a significant reduction if jumping has been determined, or by a slight increase if no jumping has been determined. In this way, it is achieved that the soil compacting device is always moved in the boundary region between jumping and not jumping.
The modification of the vibration amplitude can be carried out constantly and continuously; here it is preferable that the reduction of the vibration amplitude take place with a stronger gradient than does the increasing. Alternatively, in particular given a digital controlling of a timing element, a clock pulse can be predetermined during which the detection device determines the state of vibration of the soil contact element. If the special state of vibration has been recognized, the amplitude of the vibration can be reduced incrementally by a first amplitude difference. However, if no special operating state has been recognized in the clock pulse, the amplitude of the vibration is increased incrementally by a second, preferably smaller, amplitude difference. The clock pulse can also be set short enough that a quasi-continuous modification of the amplitude of the vibration results.
The controlling according to the present invention of the frequency of the vibration is based on the idea that the predetermined drive power, for example that delivered by a drive motor, for the soil compacting is always to be exploited optimally, i.e., to the maximum extent. For this purpose, the drive power delivered to the vibration generator is determined using a power determination device, and is compared with a target value, namely the previously determined value for an optimal drive power, and the frequency controlling device maintains the determined actual drive power in the region of the predetermined value by correspondingly adapting the frequency produced by the vibration generator.
Though the amplitude control unit and the frequency control unit each by themselves already provide a significant improvement of known control devices, and in particular provide an increase in operational efficiency, a coupling of the two control units makes further improvement possible.